HIMYM - S06e05 - Architect of Destruction on air 2010, Oct. 18

"All I knew about Jennifer Morrison was this audition that she gave that was really funny and cute," Bays said. "She and Josh did a chemistry read together and they were fantastic. ...[After her guest role was announced, there was a huge reaction], 'Jennifer Morrison's on "How I Met Your Mother"!' I think only then did I realize how much of a fan base she has."